Psoriasis is a disease for which new modalities of treatment are needed, especially for chronic, plaque-type lesions with limited skin distribution. Patients and physicians alike are frustrated because none of the existing therapies is completely satisfactory. Preliminary clinical studies indicate that psoriatic plaques, like cancer tumors, may be cleared as a result of being heated to temperatures in the hyperthermic range (42 degrees C- 46 degrees C). Proposed is the development of a relatively simple and inexpensive hyperthermia system capable of treating lesions of psoriasis and other heat-sensitive skin disease. The device will be a portable, self-contained, microprocessor-controlled system well suited for use in a dermatologist's office. The unit will be capable of producing tailored thermal distributions in skin tissues by dynamically and simultaneously controlling the acoustic frequency and power output of an ultrasound transducer and the temperature of the water bath that couples the energy to the body. Phase I of this project seeks to demonstrate the feasibility of this concept by fabricating a clinically useful treatment applicator and testing its performance in both instrumented phantoms and psoriatic tissues. Key to the success of this phase is the development of a transducer capable of efficiently radiating and withstanding continuous, high-power outputs over the frequency range of 5 MHz to 10 MHz. A novel design has been conceived and its acoustical and electrical properties simulated using a proprietary transducer modeling program developed by UltraThermics. Based on Phase I results, Phase II will request funding to develop the dedicated electronics package and cooling-fluid hardware necessary to conduct thermal dosimetry studies and clinical trials. From these investigations, it is anticipated that optimized treatment protocols will emerge that confirm the safety and efficacy of this new therapy, and thereby create a demand for commercial systems.